Category

Published on

08 Jul 2016

Abstract

Quantum dots can be produced in a variety of material systems and geometries. This educational tool simulates particle in a box problem for a variety of geometries such as boxes, cylinders, pyramids, and ellipsoids and multilayer structures composed of substrate, wetting layer, quantum dot and capping layer. Users can choose between simple single band effective mass model, two band effective mass model and 10 band sp3d5s* tight binding model (with spin-orbit coupling) and run interactively. 3-D visualization depicts the 3-D confined wave functions. Optical transitions are computed and sorted into dark and light lines. Absorption curves are computed for different polarizations and orientations. Parameters such as incident light angle and polarization, Fermi level, or temperature can be scanned to analyze the effect of 3-D geometries on isotropic optical properties. The simulation is fully parallelized and depending on the device structure, the tool decides the computational resource to be used for the simulation. This tool is supported by variety of different materials:

Ver 1.1: Now users can select an effective mass of the quantum dot. Also the tool speed was a bit improved and there is a status bar indicating progress in the visualization preparation – which had been slow.

Ver 1.1.1: The optical absorption lines are not as finely resolved and therefore do not demand such large file sizes. The default absorption line width was also increased by a factor of 10. Finally the number of allowed states was increased to 150.

Ver 1.1.4: Added default values for effective mass for the different materials listed.

Ver 2.0: The tool now runs NEMO 5 instead of NEMO 3D. This fixes a problem connected to the absolute position of energy levels. A 1s tight-binding band structure model is used which is equivalent to an effective-mass model. The optical matrix elements and absorption peaks are calculated slightly differently compared to the old tool. The GUI has been rearranged, allowing for the effective mass parameters to be set by the user. The tab for optical calculations has also been cleaned up. The performance of NEMO 5 is still undergoing optimizations.

Ver 2.0.1/2: 4 digits of floating point is used in energy states plot. Fixed error when the different number of states is used. Several detailed description of input parameters is updated.

Ver 2.1: Update to NEMO 5 r4228.

Ver 3.0: Update to NEMO 5 r17881. The tool can now simulate both particle in a box problem and multilayer structures composed of substrate, wetting layer and a capping layer. Also, the users can now choose between a single band effective mass model, 2 band effective mass model and 10 band sp3d5s* tight binding simulation. The tool can submit jobs to clusters for large simulations.

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Quantum Dot Lab version 1.x ran NEMO-3D. Starting from version 2.0, the underlying engine is NEMO 5, a code under development in the research group of Gerhard Klimeck. NEMO 5 is an open source nanoelectronics device simulator containing a variety of different material and geometry models. Features include the construction of atomistic grids of varying crystal structures, multiband Schroedinger-Poisson simulations, and user-friendly input/output.